In the case of a heavy duty tire for example, in generally, its tread profile shape (a) is formed into a single arc shape in a vulcanization die as schematically shown in FIG. 13.
In a normal internal pressure state in which such a tire is mounted on a regular rim and a normal internal pressure is charged into the tire, however, there is a tendency that a tread surface swells radially outward in a region Y separated from a tire equator by a distance which is 0.4 to 0.7 times a half of a ground-contact width of the tread. Therefore, a circumferential length difference between the swelling portion (b) and the tread ground-contact edge (e) becomes great, a slip is generated between the tread surface on the tread ground-contact edge side and a road surface, and uneven wear such as so-called unbalanced wear is prone to be generated.
To suppress the unbalanced wear, Japanese Patent Application Laid-open No.H7-164823 and the like propose a technique. In this technique, the tread profile shape is formed into a double radius shape in which a portion of the tire on the tread ground-contact edge side is of arc having a radius of curvature greater than that on the tire equator side, so that the tread profile shape in the normal internal pressure becomes closer to a single arc shape, thereby suppressing the unbalanced wear.
According to this technique, however, there is a problem that although the unbalanced wear is suppressed to a certain degree, new uneven wear is generated in the region Y. Especially when a shoulder groove is disposed in the region Y, there is a tendency that so-called orbital wear which is caused on a groove side edge of the shoulder groove appears seriously, and a satisfactory result for equalizing the wear can not be obtained.
The present invention has been accomplished in view of such problems, and it is an object of the invention to provide a heavy duty tire capable of suppressing uneven wear such as unbalanced wear and orbital wear and capable of achieving a high level of equalization of the wear based on an idea that a profile line of the ground-contact surface shape is limited.